Nonhuman primates of the species Erythrocebus patas (patas), Macaca mulatta (rhesus), and Macaca fascicularis (cynomolgus) are subjected to direct-acting and metabolism-dependent chemical carcinogens by transplacental or direct exposure. In some cases the carcinogen-treated animals are subsequently exposed to chemicals that promote the development of neoplasms in rodents. Mechanisms of organ and species differences in the effects of chemical carcinogens and tumor promoters among rodent and nonhuman primate species are investigated. Induced tumors are evaluated by light microscopy using standard staining procedures, hostochemical techniques and electron microscopy and are assayed for in vitro cultivability and transplantability to rodents.